Texture Painting not working on some parts
Its because your mesh is not unwrapped correctly. Check out this link to know how to unwrap a mesh --&gt;  Painting a dog with texture paint, TOTAL NOOB

I've tried unwrapping your mesh but the sword shell mesh was not good, its mesh was overlapping. So i've just unwrapped blade and handle.

1st mark the seam using Ctrl+E and then U and Select Unwrap.

This is how a mesh is unwrapped. It should not be overlapped, unless you want same texture on it.

I'm not a teacher but here are some Remarks after seeing the mesh :
Try making different objects in this case eg., sword,shell,handle etc.,then and after its texturing is done (or) applying the materials, join the objects into single object using Ctrl+J. Don't make everything in same object from the start.
Hope your problem is solved.